<template>
    <ul class="list">
        <li class="item" 
        v-for="item of letters" 
        :key="item" 
        :ref="item"
        @click="handleLetterClick"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        >{{item}}</li>
    </ul>
</template>
<script>
export default {
    name: 'CityAlphabet',
    props:{
        cities: Object
    },
    computed: {
        letters () {
            const letters = []
            for (let i in this.cities) {
                letters.push(i)
            }
            return letters
        }
    },
    data () {
        return {
            touchStatus:false,
            startY:0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick (e) {
            this.$emit('change', e.target.innerText)
        },
        handleTouchStart () {
            this.touchStatus = true
        },
        handleTouchMove (e) {
            if (this.touchStatus) {
                if (this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                    const touchY = e.touches[0].clientY - 79
                const index =Math.floor((touchY - this.startY) / 20)
                if (index >= 0 && index <this.letters.length) {
                    this.$emit('change', this.letters[index])
                }
                },16)    
            }
        },
        handleTouchEnd () {
            this.touchStatus = false
        }
    }
}
</script>
<style lang="stylus" scoped>
    @import '~styles/varibles.styl';
    .list
        display:flex
        flex-direction:column
        justify-content:center
        position:absolute
        right:0
        top:1.58rem
        bottom:0
        width:.4rem
        .item
            line-height:.44rem
            text-align center
            color:$bgColor
</style>


